The overall objective of this research is directed toward the adsorption of water on bone mineral and its synthetic analogs such as apatite, amorphous calcium phosphate, and octacalcium phosphate. In the current year we have been especially concerned with the temperature programmed dehydration of the various calcium phosphates. The effluent water vapor is either (1) carried off in a stream of dry helium and observed by a Gow-Mac thermal conductivity detector or (2) pumped off at 10 to the minus 6th power torr pressure and detected by a mass spectrometer. Either method makes it possible to "finger-print" the effluent gas over a temperature range from 20 degrees to 800 degrees C. The results may be interpreted in comparison with other means of study of the dehydration process such as x-ray diffraction and infrared spectroscopy. The dehydration in most cases is rather complex and is due not only to desorption of adsorbed water but also to decomposition of OH- containing groups in the phosphates and in some cases to water of crystallization as in octacalcium phosphate. In favorable cases it is possible to derive the energies of activation for these dehydration processes. In the coming year it is planned to complete the measurements on the samples already studied and to extend them to two series of calcium deficient apatites. A study of carbonate apatites will also be undertaken.